Star-Shaped ESIPT-Active Mechanoresponsive Luminescent AIEgen and Its On-Off-On Emissive Response to Cu2+/S2-

Design and development of multifunctional materials have drawn incredible attraction in recent years. Herein, we report the design and construction of versatile star-shaped intramolecular charge transfer (ICT)-coupled excited-state intramolecular proton transfer (ESIPT)-active mechanoresponsive and aggregation-induced emissive (AIE) luminogen triaminoguanidine-diethylaminophenol (LH3) conjugate from simple precursors triaminoguanidine hydrochloride and 4-(N,N-diethylamino) salicylaldehyde. Solvent-dependent dual emission in nonpolar to polar protic solvents implies the presence of ICT-coupled ESIPT features in the excited state. Aggregation-enhanced emissive feature of LH3 was established in the CH3CN/water mixture. Furthermore, this compound exhibits mechanochromic fluorescence behavior upon external grinding. Fluorescence microscopy images of pristine, crystal, and crushed crystals confirm the naked-eye mechanoresponsive characteristics of LH3. In addition, LH3 selectively sensed a Cu2+ ion through a colorimetric and fluorescence turn-off route, and subsequently, the LH3-Cu2+ ensemble could act as a selective and sensitive sensor for S2- in a turn-on fluorescence manner via a metal displacement approach. Reversible turn-off-turn-on features of LH3 with Cu2+/S2- ions were efficiently demonstrated to construct the IMPLICATION logic gate function. The Cu2+/S2--responsive sensing behavior of LH3 was established in the paper strip experiment also, which can easily be characterized by the naked eye under daylight as well as a UV lamp (lambda = 365 nm).